1. Field of the Invention
The present invention relates to an electron spin resonance (ESR) measuring apparatus, and more particularly to a ferromagnetic resonance (FMR) measuring apparatus and a cavity resonator to be used in the ferromagnetic resonance measuring apparatus.
2. Description of the Related Art
A ferromagnetic resonance (FMR) measurement is a kind of electron spin resonance (ESR) measurement and is employed for evaluating the magnetic properties of a magnetic material.
In the ferromagnetic resonance measurement, a cavity resonator having a cavity portion enclosed by a side wall is used. Microwaves are introduced into the cavity resonator, and a small spherical specimen or a small disk specimen is positioned where the intensity of the high-frequency magnetic field is maximum within the cavity resonator. Ferromagnetic resonance is caused by applying a static magnetic field while at the same time varying its strength. Based on measured ferromagnetic resonance signals, the resonance magnetic field, the ferromagnetic resonance half-value width, the saturation magnetization, the anisotropy field and the like are obtained.
As for ferromagnetic single crystals having a narrow ferromagnetic resonance half-value width, the aforementioned method using a cavity resonator is not used. Since a material having a narrow ferromagnetic resonance half-value width gives a high signal strength, a slight frequency variation in the cavity resonator may be the cause of a major error when ferromagnetic resonance takes place in the cavity resonator equipped with such a material. Thus, precise ferromagnetic resonance signals cannot be detected. In connection with ferromagnetic single crystals having a narrow ferromagnetic resonance half-value width, the cavity resonator has difficulty measuring the true value of the ferromagnetic resonance half-value width. It is contemplated that ferromagnetic resonance half-value width is measured by reducing the volume of a specimen to be as small as possible to make the relative signal strength small. For example, in the case of a ferromagnetic single crystal film wafer specimen that is epitaxially grown on a substrate having a size of a few centimeters across, the wafer specimen is cut into an individual 1 mm by 1 mm chip. This small chip is positioned inside the cavity resonator and ferromagnetic resonance half-value width is measured.
The conventional method has drawbacks. Specifically, in order to control the ferromagnetic resonance half-value width of ferromagnetic single crystal film wafers which are mass-produced, a small chip must be cut from each individual wafer. Thus, the cutting of small chips requires additional time thereby increasing the time required for measurement. Since a small chip is cut from an individual wafer, the yield of the chip production for devices from the wafer is also degraded. In addition, although the ferromagnetic resonance half-value width of a small chip cut from the wafer can be measured, the ferromagnetic resonance half-value width in a wafer having a larger area cannot be measured.
In order to solve the above problems, Japanese Laid-open Patent Application No. 63-73174 discloses a method of using a waveguide having a non-reflective terminal on one end and IEEE Transactions on Magnetics, 25, 3488-3490, 1989 discloses a method of using a short-circuit waveguide. In these methods, ferromagnetic resonance half-value width is measured without the need for cutting small chips from a ferromagnetic single crystal film wafer measuring a few centimeters wide. Although in the former method, a commercially available electron spin resonance measuring instrument can be used for measurement with the cavity resonator section replaced with a waveguide having a non-reflective terminal, ferromagnetic resonance measurements at arbitrary positions on the wafer is difficult because the ferromagnetic single crystal film wafer itself becomes a resonator. For this reason, this method is not suitable for the control of the ferromagnetic resonance half-value width of the ferromagnetic single crystal film wafer in practice. The latter method fails to present circuit compatibility with any commercially available electron spin resonance measuring instrument, and thus a new measuring system must be constructed.